Subban spent his junior career with the Belleville Bulls of the Ontario Hockey League (OHL). In 2005–06 he recorded 12 points in a 52-game rookie campaign. In 2006–07, he improved to 56 points in 68 games, where he was later drafted by the Canadiens in the off-season at the 2007 NHL Entry Draft. Subban then recorded 46 points in just 58 games during the 2007–08 campaign, before adding 23 points and matching his regular season goals total of eight in the post-season. He helped Belleville to the J. Ross Robertson Cup Finals against the Kitchener Rangers, where they lost the OHL title in seven games. Subban finished his four-year junior career with 76 points in 56 games in the 2008–09 regular season, with the Bulls advancing to the league playoffs, losing in the OHL semi-finals.

In May 2009, two weeks after his last junior game, Subban was signed to a three-year, entry-level contract by the Canadiens.[2] He began the 2009–10 season with the Hamilton Bulldogs, Montreal's American Hockey League (AHL) affiliate. Later in the season, he was then selected to play in the 2010 AHL All-Star Game in Portland. Shortly thereafter, he earned his first call-up to the Canadiens on February 11, 2010, and, on the following day, registered his first career NHL point, an assist, in his debut against the Philadelphia Flyers on February 12.

On April 26, 2010, Subban was recalled from Hamilton during the Canadiens' first round Stanley Cup playoff series against the Washington Capitals.[3] He recorded his first NHL playoff point, an assist, in his first career NHL playoff game, on April 26.[4] His first goal came in Game 1 of the Canadiens' second round series against the Pittsburgh Penguins on April 30, 2010.[5] In Game 3 against the Philadelphia Flyers in the 2010 Eastern Conference Finals, Subban became the third rookie defenceman in Canadiens history to register three assists in one game.[6] In all, Subban recorded one goal and eight points in 14 playoff games for the Canadiens, who ultimately fell to Philadelphia.

After the Canadiens were eliminated by the Flyers, Subban was returned to the Bulldogs, who were still in contention in the Calder Cup playoffs.[7] At the end of the AHL season, Subban was awarded the AHL President's Award in recognition of his accomplishments for the year.[8]

On March 20, 2011, Subban became the first Canadiens rookie defenceman to score a hat-trick in a game, which came in an 8–1 victory over the Minnesota Wild.[9]

Playing in 81 games in the 2011–12 season, Subban recorded seven goals and 29 assists. A restricted free agent after the season, Subban sat out the first four games of the 2012–13 season, which was postponed until January 2013 due to a labour lock-out, while the two sides negotiated a contract. On January 28, 2013, however, Subban eventually signed a two-year, $5.75 million deal with Montreal.[10] He scored 11 goals and 27 assists, matching his career-high 38 points despite playing in only 42 games due to the lock-out. At the end of the season, he was awarded with the James Norris Memorial Trophy as the NHL's defenceman of the year, edging-out Kris Letang and Ryan Suter for the honour.[11] On July 3, 2013, Subban was named to the NHL First All-Star Team.

Subban then played all 82 games during the 2013–14 regular season, in which he registered a total of 53 points, ten of which were goals. During the 2014 playoffs, he was one of Montreal's most important assets, registering 14 points in 17 games as the Canadiens ultimately reached the Eastern Conference Finals, falling to the New York Rangers.

Subban became a restricted free agent at the close of the 2013–14 season when his contract expired. According to the NHL Collective Bargaining Agreement (CBA), Subban earned the right to salary arbitration, having signed his first Standard Player Contract between the ages of 18 and 20 and having accrued four years of professional experience or more.[12] He subsequently filed for arbitration before the deadline of July 5.[13] The hearing took place on August 1, 2014, with Subban's camp asking for a one-year deal worth $8.5 million, while the Canadiens offered a one-year deal worth $5.5 million.[14]

Under NHL CBA rules, the parties could continue to negotiate and reach an agreement until the arbitrator announced her decision, given in the 48 hours following the hearing. As arbitration was player-elected, once the arbitrator released her decision, the team would have had 48 hours to agree to the terms or walk away from the player, thereby making Subban an unrestricted free agent.[12] The day after the hearing, on August 2, it was announced that Subban and the Habs had agreed to terms on an eight-year, $72 million contract, running through the 2021–22 season.[15] The contract made him the highest-paid defenceman in the NHL and third-highest paid League player overall at the time.[16]

Subban made an international debut for Canada at the 2008 World Junior Ice Hockey Championships in the Czech Republic. He saw limited ice time as Canada's seventh defenceman, but was able to help the team capture their fourth consecutive gold medal at the tournament, defeating Sweden in overtime in the final. Subban again represented Canada at the 2009 World Juniors in Ottawa, taking on a more central role with the team. He scored three goals and nine points and a differential of +12 in the tournament, helping Canada to its fifth consecutive gold medal as they once again defeated Sweden in the final. Subban was named to the Tournament All-Star Team, along with tournament MVP and close friend John Tavares.

Subban was invited to participate in the 2012 IIHF World Championship, but was injured during pre-tournament play. In the next season, Subban was a late addition to the Canadian team at the 2013 edition of the tournament; he joined them in the elimination round for one game, which Canada lost. On January 7, 2014, Subban was named to Canada's 2014 Winter Olympic team for participation in the Games in Sochi in defence of their 2010 gold medal.[19] They successfully reprised the gold, prevailing 3–0 over Sweden in the tournament final.

Before the 2015–16 season, on September 16, 2015, Subban announced his donation of $10 million to the Montreal Children's Hospital.[20] The hospital called it "the biggest philanthropic commitment by a sports figure in Canadian history."[20] After his donation, Subban continued his commitment as spokesman and organized the Winter Wonderland with Air Canada at the hospital before the holidays.[21]